MILWAUKEE -

A special prosecutor has been named to oversee the investigation into the death of a man who died in Milwaukee police custody.

Former Milwaukee County Circuit Judge John Franke was appointed Tuesday to oversee the public inquest into the death of Derek Williams.

Williams died in July 2011, gasping for air in the back of a Milwaukee police squad car.

The Milwaukee County medical examiner's office initially ruled Williams' death natural. But the medical examiner changed the death to a homicide after the Milwaukee Journal Sentinel presented police reports and squad video of Williams struggling to breathe.

The Journal Sentinel reports Chief Judge Jeffrey Kremers appointed Franke, a former judge now in private practice. Milwaukee District Attorney John Chisholm says Franke has agreed to handle the matter for free.